Subcellular redistribution of la/SSB autoantigen during physiologic apoptosis in the fetal mouse heart and conduction system: a clue to the pathogenesis of congenital heart block

OBJECTIVE

In isolated congenital heart block, the mechanism by which maternal autoantibodies target the intracellular components of the Ro/La RNP complex is unclear. Previous studies have demonstrated that cultured fetal cardiac myocytes rendered apoptotic bind antibodies to 48-kd La/SSB. This study further investigated the subcellular distribution of the La antigen during apoptosis in the fetal mouse heart and conduction system.

METHODS

The atrioventricular (AV) node, AV bundle, and sinoatrial (SA) node were identified in serial sections prepared from paraffin blocks of normal mouse fetuses on days 15, 17, and 19 of gestation. Apoptosis was detected by TUNEL assay. Under confocal microscopy, fluorescent labeling of fragmented DNA in apoptotic cells was assessed by TUNEL, and La protein localization was visualized simultaneously using a murine monoclonal antibody or affinity-purified human polyclonal anti-La antibodies.

RESULTS

Apoptotic cells were detected in and at the periphery of the AV and SA nodes as well as in the fetal heart valve insertions and working myocardium. In contrast, no apoptosis was detected in the adult heart AV node or surrounding myocardium. As expected, the La antigen was predominantly immunolocalized to the nucleus in nonapoptotic cells. However, apoptotic cells showed a marked reduction of nuclear La and redistribution of La to the cytoplasm. High-resolution confocal microscopy revealed that in cells that had undergone apoptosis, La antigen asymmetrically clustered near the surface of TUNEL-positive nuclei and apoptotic bodies.

CONCLUSION

These data provide the first in vivo demonstration of the subcellular translocation of La autoantigen during apoptosis in the fetal heart and the conduction system under physiologic conditions. This observation supports the hypothesis that subcellular redistribution of La in the normally developing heart facilitates the binding of cognate maternal antibodies and subsequent tissue damage.

Subcellular distribution of aquaporin 5 in salivary glands in primary Sjögren's syndrome

Secretions from salivary and lacrimal glands are reduced in patients with primary Sjögren's syndrome (PSS). Since aquaporin 5 is involved in transport of water and is present in salivary and lacrimal glands, this protein was thought to have a major role in the pathogenesis of PSS. We used indirect immunofluorescence and an immunoperoxidase technique to assess expression and subcellular localisation of aquaporin 5 in patients and controls. Our results suggest that the distribution and density of aquaporin 5 in salivary glands does not differ between patients with PSS and those without. Thus, the role of aquaporin 5 in the pathogenesis of PSS needs to be reassessed and alternative pathogenetic mechanisms investigated.

Cognate T cell help is sufficient to trigger anti-nuclear autoantibodies in naive mice

The mechanisms involved in the initiation of anti-nuclear autoantibodies are unknown. In this study, we show that one factor allowing anti-nuclear autoantibodies to develop is the incomplete nature of immune tolerance to many of these proteins. Immune responses in mice toward the ubiquitous nuclear autoantigen La/SS-B are much weaker than responses to the xenoantigen, human La (hLa; 74% identical). However, in transgenic (Tg) mice expressing hLa, the Ab response to this neo-autoantigen was reduced to a level resembling the weak autoimmune response to mouse LA: Partial tolerance to endogenous La autoantigen was restricted to the T compartment because transfer of CD4(+) T cells specific for one or more hLa determinants into mice bearing the hLa transgene was sufficient to elicit production of anti-hLa autoantibodies. Notably, only hLa- specific T cells from non-Tg mice, and not T cells from hLa Tg mice, induced autoantibody production in hLa Tg mice. These findings confirm partial Th tolerance to endogenous La and indicate the existence in normal animals of autoreactive B cells continuously presenting La nuclear AG: Therefore, the B cell compartment is constitutively set to respond to particular nuclear autoantigens, implicating limiting Th responses as a critical checkpoint in the development of anti-nuclear autoantibodies in normal individuals.

Current concepts on diagnosis, autoantibodies and therapy in Sjögren's syndrome

Sjögren's syndrome is a chronic autoimmune and rheumatic disorder. Most patients have mild to moderate complaints and this may explain the great discrepancy in prevalence found in population studies compared to studies performed in the clinic. However, there is no straightforward and simple diagnostic test for Sjögren's syndrome, although several classification criteria have been designed. Initiatives have been taken to propose a new set of classification criteria in a joint effort by research groups in Europe and USA. A large number of autoantibodies have been reported in Sjögren's syndrome where, in some cases, the antibodies are correlated with the extent and severity of disease. The finding of serum autoantibodies directed against the muscarinic M3 receptor is an important advance in understanding the pathogenesis of not only the impaired glandular function but also associated features of autonomic dysfunction in some patients. The treatment of primary Sjögren's syndrome is still mainly symptomatic.

Can B cell epitopes of 60 kDa Ro distinguish systemic lupus erythematosus from Sjögren's syndrome?

Antibodies binding components of the Ro/La (or SSA/SSB) ribonucleoprotein particle are found in the sera of patients with systemic lupus erythematosus (SLE) and Sjögren's syndrome (SS) as well as mothers who give birth to babies with neonatal lupus. Anti-La occurs in a subset of sera that contain anti-Ro, and anti-La is found more commonly in sera of patients with SS than in sera from SLE patients. The fine specificity of autoantibodies binding 60 kDa has been studied extensively. Recent data have suggested that there are disease-specific epitopes which identify patients with either SLE or SS. Alternatively, other data suggest that the B cell epitopes of 60kDa Ro vary according to the presence of anti-La. The present study was undertaken to determine whether binding of putative disease-specific 60 kDa Ro epitopes is associated with the diagnosis of SLE vs SS, or instead associated with the presence of anti-La. Anti-60 kDa Ro positive sera from 24 SLE patients and 44 SS patients were studied for antibodies binding two epitopes of 60 kDa Ro. We find the epitope defined by residues 171-190 is associated with anti-60 kDa Ro without anti-La, regardless of diagnosis. Meanwhile, binding of the epitope defined by residues 215-232 is not commonly found in anti-60 kDa Ro sera, especially in those sera with both anti-60 kDa Ro and anti-La. Thus, the fine specificity of antibody binding to 60 kDa Ro varies according to the presence of anti-La, not to the diagnosis of either SLE or SS.

Antibodies to AB blood group antigens mimic anti-salivary duct autoantibodies in patients with limited sicca symptoms

OBJECTIVE

We evaluated the clinical relevance and pathogenic significance of anti-salivary duct autoantibodies (ASDA) in Sjögren's syndrome (SS) and rheumatoid arthritis (RA) by examining (1) their frequency in healthy controls, patients with sicca symptoms, and patients with various autoimmune and infective disorders; (2) their localization by confocal microscopy; and (3) their tissue distribution and cross reactivity with blood group antigens.

METHODS

Indirect immunofluorescence (IF) was performed on commercial cryostat sections of monkey parotid salivary gland. Sections were examined by fluorescence and confocal laser scanning microscopy. Sera giving positive staining on the ducts were tested by IF on a range of monkey tissues and salivary glands from several mammalian species. Blocking experiments were performed with human erythrocytes of different ABO blood groups and AB antigens.

RESULTS

We identified 2 distinct ductal staining patterns. The first resembled ASDA described in earlier studies and showed patchy bright staining of the apical (luminal) surfaces of the ducts and staining of apical cytoplasmic vesicles. The other was only observed with anti-mitochondrial antibody positive sera and stained the mitochondrial-rich ductal epithelium in a distinctive punctate pattern. Antibodies staining the apical surface of ducts were detected rarely in patients with antiRo/La autoantibody-positive primary SS (1/76) and RA (1/36) and were found in only 1115 with RA and secondary SS. ASDA were detected in sera from 13/51 (25.5%) of patients referred to our clinic with limited sicca symptoms who were anti-Ro/La antibody-negative and had no typical clinical or laboratory features of classical primary SS. The apical ductal staining pattern was not observed with sera from 63 healthy controls without sicca symptoms or in patients with autoimmune and infective disorders. Twelve of the 13 patients whose sera gave ASDA-like staining were blood group O and one group A. Ductal staining was abolished in all sera after absorption with blood group AB erythrocytes or AB antigen. In 5 patients ductal staining was removed by absorption with B erythrocytes but not with A erythrocytes; in the remainder ductal reactivity was abolished by both A and B erythrocytes.

CONCLUSION

ASDA seem to occur rarely in patients with primary SS and RA. However, isotype-switched IgG AB blood group antibodies cross react with primate salivary ducts and may produce false positive ASDA staining. Detection of ASDA may be of value in identifying a subset of patients who present with mild sicca symptoms without other autoimmune features.

Inhibitory effects of muscarinic receptor autoantibodies on parasympathetic neurotransmission in Sjögren's syndrome

OBJECTIVE

Sjögren's syndrome (SS) is an autoimmune disorder characterized by dry eyes and mouth (sicca syndrome) and lymphocytic infiltration of the lacrimal and salivary glands. Abnormalities of parasympathetic neurotransmission may contribute to the glandular dysfunction. In this study, we used a functional assay to investigate autoantibody-mediated effects on parasympathetic neurotransmission and smooth muscle contraction.

METHODS

Serum and purified IgG were obtained from patients with primary and secondary SS and from control subjects. Contraction of isolated bladder strips in response to stimulation of M3-muscarinic receptors by a muscarinic receptor agonist, carbachol, or by endogenous acetylcholine released from postganglionic parasympathetic nerves was measured before and after the addition of patient serum or IgG.

RESULTS

Sera from 5 of 9 patients with primary SS and from 6 of 6 patients with secondary SS inhibited carbachol-evoked bladder contraction by approximately 50%. Sera from these patients also inhibited the action of neuronally released acetylcholine at M3-muscarinic receptors. Sera from 7 of 8 healthy individuals, from patients with rheumatoid arthritis without sicca symptoms, and from patients with systemic lupus erythematosus had no effect. The anti-muscarinic receptor activity was localized in the IgG fraction, since purified IgG from patients with SS also inhibited agonist- and nerve-evoked contractions. In this preliminary study, the autoantibodies seemed to be associated with the presence of bladder symptoms and other autonomic features.

CONCLUSION

Autoantibodies that act as antagonists at M3-muscarinic receptors on smooth muscle occur in a subset of patients with primary and secondary SS. Their presence in secondary SS was unexpected and provides new evidence for a common pathogenetic link between primary and secondary SS. These autoantibodies appear to contribute to sicca symptoms and may explain associated features of autonomic dysfunction in some patients.

Activity of the hypothalamic-pituitary-adrenal axis is altered by aging and exposure to social stress in female rhesus monkeys

Age-related changes in glucocorticoid negative feedback inhibition of hypothalamic CRF and pituitary ACTH are observed in rodents. Attempts to study similar effects in humans have produced mixed results due in part to the difficulty in matching older subjects on social and lifestyle variables. The present study used female rhesus monkeys as a model for women by comparing young adult (n = 20) to old (n = 20) females to test the hypotheses that the hypothalamic-pituitary-adrenal axis is altered in older animals and that this difference is exacerbated by exposure to social stress. The effects of age on the response to two doses of dexamethasone and two doses of CRF were assessed in females living in a stable social environment (control) and in socially stressed females removed from their group and housed temporarily in a remote, nonsocial environment (separated). The suppression of serum cortisol was not different between the two doses of dexamethasone. Before dexamethasone administration (2100 h), serum cortisol was significantly higher in old control females than in either young or old separated females, who were not different from one another. The young control females had baseline cortisol concentrations significantly lower than all other groups. Serum cortisol was suppressed approximately 75% below baseline values in all groups by 10 h after dexamethasone administration. Age significantly affected serum cortisol after dexamethasone, as the old control group showed a release from suppression 19 h posttreatment compared to the young control group and compared to the separated groups. Social condition had a significant effect on the responses of serum cortisol and plasma ACTH to CRF administration. At baseline (0930 h), serum cortisol was significantly higher in young controls compared with older controls, with both separated groups having intermediate values. Similarly, plasma ACTH at baseline was significantly higher in young controls compared to all other groups. Social separation significantly diminished the elevation of both serum cortisol and ACTH after stimulation with either dose of CRF. Control females showed a prolonged increase in plasma ACTH through 60 min and an increase in serum cortisol through 120 min after CRF. In contrast, these hormones either declined by 60 min or did not increase in socially separated females after CRF administration. These data suggest that the circadian rhythm in serum cortisol may be affected by aging, as levels were higher in the evening and lower in the morning in old control compared to young control females. The effect of age on the response to dexamethasone treatment among the control groups lends support to the hypothesis that the sensitivity of glucocorticoid negative feedback diminishes with aging. Although age did not affect the response to CRF, social separation diminished the elevation in both serum cortisol and plasma ACTH. Whether this effect was due to stress-induced down-regulation of pituitary CRF receptors remains to be determined.

Anti-calreticulin segregates anti-Ro sera in systemic lupus erythematosus: anti-calreticulin is present in sera with anti-Ro alone but not in anti-Ro sera with anti-La or anti-ribonucleoprotein

OBJECTIVE

To examine a well characterized group of patients with systemic lupus erythematosus (SLE) for anti-calreticulin.

METHODS

The sera of 77 patients with SLE were studied by immunodiffusion, solid phase immunoassay, and immunoblot for antibodies against ribonucleoprotein (RNP) autoantigens and calreticulin.

RESULTS

Thirty-five had anti-calreticulin and 40 had anti-60 kDa Ro. There was no association of anti-60 kDa Ro and anti-calreticulin. However, among anti-60 kDa Ro positive sera that also contained either anti-La or anti-RNP, none of 18 had anti-calreticulin. All the remaining sera with anti-60 kDa Ro had anti-calreticulin and anti-52 kDa Ro.

CONCLUSION

Anti-60 kDa Ro patients with SLE can be divided into those with anti-60 kDa Ro and either anti-La or anti-RNP or those with anti-60 kDa Ro, anti-52 kDa Ro, and anti-calreticulin.

Cerebral white matter lesions in primary Sjögren's syndrome: a controlled study

OBJECTIVE

To determine the prevalence of neurological and magnetic resonance imaging (MRI) abnormalities in a well defined population of unselected patients with primary Sjögren's syndrome (SS) and age and sex matched healthy patients.

METHODS

Thirty patients with SS and 29 age and sex matched controls were examined by a neurologist and subsequently underwent MRI scanning with a 1.0 Tesla Siemens Impact MR scanner. Scans were graded by a neuroradiologist blinded to the clinical status of each subject. The number and location of white matter lesions > 3 mm in long axis (to exclude non-specific perivascular changes) were recorded for each subject.

RESULTS

There was a significant increase in lesions detected by MRI in SS patients versus controls (p = 0.02) including deep white matter lesions (p = 0.03) and subcortical white matter lesions (p = 0.02). The presence of white matter lesions did not correlate with serum IgG or rheumatoid factor levels, or with presence of anticardiolipin antibodies. No subjects had symptoms or signs of serious neurological disease including multiple sclerosis, and corpus callosal lesions commonly seen in multiple sclerosis were notably absent in this study.

CONCLUSION

Cerebral white matter lesions detected by MRI are more frequent in patients with primary SS than control subjects, yet do not appear to be associated with significant clinical manifestations. Although the pathological nature of these lesions is yet to be defined, their presence should not be over-interpreted.

Induction of autoimmunity by multivalent immunodominant and subdominant T cell determinants of La (SS-B)

We investigated the consequences of altering the form and valence of defined autodeterminants on the initiation and spreading of experimentally induced La/Ro autoimmunity. Anti-La and Ro (SS-A) Ab responses were monitored following immunization of healthy mice with defined immunodominant and subdominant T cell determinants of the La (SS-B) autoantigen synthesized as either monomeric or multiple antigenic (MAP) peptides. Abs to mouse La (mLa) developed faster and were of higher titer in mice immunized with the subdominant mLa25-44 MAP compared with mice immunized with the 25-44 monomer. Rapid intermolecular spreading of the autoimmune response to 60-kDa Ro was observed in AKR/J mice immunized with mLa25-44 MAP, but not in mice immunized repeatedly with monomeric peptide. A/J mice immunized and boosted with the known tolerogenic mLa287-301 determinant delivered as monomeric peptide failed to develop Abs to either intact mLa or mLa287-301 peptide. However, immunization with the multivalent mLa287-301 peptide led to the rapid production of high titer mLa autoantibodies associated with a proliferative T cell response to the mLa287-301 peptide. The data suggested that the enhanced immunogenicity of MAPs was not due to augmented Ag presentation or T cell stimulation. However, MAP-, but not monomer peptide-, containing immune complexes were potent substrates for Ab-dependent fixation of complement. These results demonstrate that the form of Ag responsible for inducing autoimmunity can profoundly influence the nature and magnitude of the immune response. Thus, molecular mimicry of tolerogenic and nontolerogenic self determinants might trigger autoimmunity under conditions of altered valence.

Induction of Autoimmunity by Multivalent Immunodominant and Subdominant T Cell Determinants of La (SS-B)

We investigated the consequences of altering the form and valence of defined autodeterminants on the initiation and spreading of experimentally induced La/Ro autoimmunity. Anti-La and Ro (SS-A) Ab responses were monitored following immunization of healthy mice with defined immunodominant and subdominant T cell determinants of the La (SS-B) autoantigen synthesized as either monomeric or multiple antigenic (MAP) peptides. Abs to mouse La (mLa) developed faster and were of higher titer in mice immunized with the subdominant mLa25–44 MAP compared with mice immunized with the 25–44 monomer. Rapid intermolecular spreading of the autoimmune response to 60-kDa Ro was observed in AKR/J mice immunized with mLa25–44 MAP, but not in mice immunized repeatedly with monomeric peptide. A/J mice immunized and boosted with the known tolerogenic mLa287–301 determinant delivered as monomeric peptide failed to develop Abs to either intact mLa or mLa287–301 peptide. However, immunization with the multivalent mLa287–301 peptide led to the rapid production of high titer mLa autoantibodies associated with a proliferative T cell response to the mLa287–301 peptide. The data suggested that the enhanced immunogenicity of MAPs was not due to augmented Ag presentation or T cell stimulation. However, MAP-, but not monomer peptide-, containing immune complexes were potent substrates for Ab-dependent fixation of complement. These results demonstrate that the form of Ag responsible for inducing autoimmunity can profoundly influence the nature and magnitude of the immune response. Thus, molecular mimicry of tolerogenic and nontolerogenic self determinants might trigger autoimmunity under conditions of altered valence.

Molecular chaperones are targets of autoimmunity in Ro(SS-A) immune mice

We have used a murine model of experimental anti-Ro(SS-A) autoimmunity to dissect additional intermolecular interactions between the 52-kD Ro (Ro52) and 60-kD Ro (Ro60) autoantigens and molecular chaperones. Immune responses to members of the heat shock protein hsp70 and hsp90 families were measured by immunoblotting and ELISA in sera from mice immunized and boosted with purified recombinant Ro52, Ro60 and La (SS-B). All Ro52 and Ro60 immune sera immunoblotted the inducible glucose-regulated protein grp78 and hsp70 species but not constitutive hsc70 or hsp90. The kinetics of antibody production and reciprocal affinity purification experiments indicated that the grp78 and hsp70 responses were cross-reactive but distinct from immune responses to the primary Ro52 and Ro60 immunogens and the endoplasmic reticulum (ER)-resident chaperone calreticulin. No responses to molecular chaperones were detected in the La-immunized mice. Control immunizations indicated that the recruited grp78 and hsp70 responses were specific for the Ro proteins and not due to immunization with denatured protein. The rapid spreading of immunity to the inducible grp78 and hsp70 in Ro52- and Ro60-immunized mice suggests that these components may co-localize and physically associate under certain physiological conditions which may promote autoimmunization. The potential importance of the ER-resident chaperones grp78 and calreticulin is further supported by their co-localization with Ro in small apoptotic membrane blebs and the finding of a novel putative grp78 binding motif in the carboxyl-terminal region of Ro52.

Determinant spreading: lessons from animal models and human disease

Spreading of the immune response is a common theme in organ-specific and systemic autoimmune diseases. We evaluated whether some of the mixed antinuclear antibody patterns characteristic of systemic autoimmunity might be the result of determinant spreading from a single initiating event. Immunisation of healthy mice with individual protein components of the La/Ro ribonucleoprotein (RNP) targeted in systemic lupus erythematosus and primary Sjögren's syndrome induced autoantibodies recognising Ro60 (SS-A), Ro52 (SS-A) and La (SS-B) and in some cases the molecular chaperones calreticulin and Grp78. The endogenous antigen(s) driving determinant spreading might be derived from physiological apoptosis which could explain the involvement of some chaperone proteins in the autoimmune response. Diversified anti-La/Ro antibody responses were initiated by challenge with a single subdominant T epitope of La even though some self epitopes of La were efficiently tolerised. The pattern of autoantibody responses in primary Sjögren's syndrome was strongly influenced by HLA class II phenotype which we speculate controls activation of T cells recognising defined peptides from the La/Ro RNP. In this way, HLA class II alleles may be critical in influencing initiation and spreading of systemic autoimmune reactions. Molecular mimicry of such determinants by exogenous agents might readily initiate spreading of an autoimmune response in genetically susceptible hosts.

Spreading of the immune response from 52 kDaRo and 60 kDaRo to calreticulin in experimental autoimmunity

Calreticulin (CR) is widely recognized as a new human autoantigen but there are conflicting data concerning its relationship with the Ro(SS-A) ribonucleoprotein (RNP). Recent evidence suggests that CR binds to 52 kDaRo (Ro52) by a protein/protein interaction and binds to hY RNA and rubella virus RNA. Other studies have shown that initiation of immunity to either Ro52 or 60 kDaRo (Ro60) can lead to reciprocal spreading of autoimmunity to Ro60 or Ro52, respectively, and induce anti-La autoantibodies in some strains of mice. These findings support a physical association of these polypeptides in Ro/La complexes. To test the hypothesis that CR is physically associated with Ro52 and/or Ro60 we examined the sera of Ro52-, Ro60- and La-immunized mice for intermolecular spreading to CR. Immune sera from BALB/c and C3H/HeJ mice immunized with recombinant 6xHis-mouse Ro52, 6xHis-human Ro60 or 6xHis-human La were tested for reactivity by ELISA and immunoblotting with a full-length human CR protein expressed as a soluble maltose binding protein fusion protein (CR-MBP). Five of the six Ro52-immunized C3H/HeJ mice sera and all six Ro60-immunized C3H/HeJ mice sera reacted with the CR-MBP (but not a MBP control) on ELISA. In the BALB/c group, the responder rate was lower with one in six of the Ro52-immunized and one in five of the Ro60-immunized mice spreading to CR. In contrast, none of the BALB/c or C3H/HeJ mice which was immunized with La showed evidence of a recruited anti-CR antibody response. Immunoblotting of the different recombinant proteins with immune sera from the C3H/HeJ mice confirmed the specificity of the initial and recruited antibody responses. The spreading of immunity from Ro52 and Ro60 to CR in Ro-immunized mice suggests that a subpopulation of CR or CR-like molecules must associate under certain circumstances with Ro52 and Ro60 polypeptides in vivo, possibly as Ro/CR complexes concentrated in surface membrane blebs of apoptotic cells. The lack of spreading to CR in La-immunized mice suggests that CR may be associated with a subpopulation of Ro particles from which La has already dissociated.

Hierarchical self-tolerance to T cell determinants within the ubiquitous nuclear self-antigen La (SS-B) permits induction of systemic autoimmunity in normal mice

Systemic autoimmune diseases are frequently associated with clustering of high titer autoantibody responses towards nuclear self-antigens. Little is known, however, about the extent of immune tolerance to the target nuclear antigens or the events leading to the complex autoantibody responses that are characteristic of systemic autoimmunity. To address these issues, we have examined the mouse immune response to La autoantigen (mLa) and the homologous human La antigen (hLa), which are components of the La(SS-B)/Ro(SS-A) ribonucleoprotein (RNP) complex targeted in systemic lupus erythematosus and primary Sjögren's syndrome. The findings reveal the presence of hierarchical T cell tolerance involving multiple autodeterminants within the La autoantigen expressed by normal H-2k and H-2a mice. At one end of this spectrum, there was no detectable T or B cell autoimmunity observed in mice that were immunized with the immunodominant mLa287-301 determinant, which differed by a single residue in its core sequence from the homologous but highly immunogenic human La288-302 determinant. Interestingly, the mLa287-301 peptide acted as an altered peptide ligand that specifically antagonized the activation of an hLa288-302-specific T cell hybridoma. In contrast to the tolerogenic mLa287-301 determinant, a range of autoimmune potential was identified among poorly tolerizing, subdominant self-peptides present within mouse La autoantigen. Notably, immunization of normal mice with the autologous subdominant La25-44 and La106-129 determinants resulted in limited or no detectable autoantibody response. In contrast, immunization with the subdominant mouse La13-30 determinant induced a proliferative T cell response associated with the appearance of specific autoantibodies recognizing multiple intrastructural (La) and intermolecular components (Ro) of the murine La/Ro RNP. The findings suggest how diversified autoimmunity might follow initiation of immunity to simple peptide mimics of poorly tolerogenic determinants that are present within ubiquitous self-antigens.

The immune response to 52-kDa Ro and 60-kDa Ro is linked in experimental autoimmunity

Clustering of autoantibody specificities is a consistent finding in patients with systemic autoimmune diseases. Patients with Sjögren's syndrome frequently have autoantibodies to La, 60-kDa Ro(SS-A) protein (Ro60), and 52-kDa Ro(SS-A) protein (Ro52). In the case of anti-Ro60 and anti-La, there is evidence that these specificities occur together because of the physical association of the Ro60 and La proteins that form a ribonucleoprotein particle (RNP). Thus, the autoantibody response may spread from a single epitope to involve new epitopes located within other components of the RNP. The physical association of Ro52 with the Ro/La RNP has remained controversial, implying that Abs to Ro52 are not a consequence of intermolecular spreading and may be triggered independently of the anti-Ro60 response. To examine this relationship of the immune response to Ro52 and Ro60, mice were immunized with recombinant Ro52, Ro60, or La, and examined for autoantibody production. Immunization with Ro52 resulted in rapid, high titer Ab production to Ro52, followed 7 to 14 days later by lower titer autoantibody production to Ro60. Immunization with Ro60 led to anti-Ro60, which was also followed 7 to 14 days later by a lower titer anti-Ro52 response. Cross-reactivity of affinity-purified Abs from immune mouse sera was not observed. These observations suggest that the autoimmune responses to Ro60 and Ro52 are linked intrinsically, despite previous evidence suggesting they are not associated in vivo. The mechanism of linkage remains unclear, but the data are most consistent with some physical association of Ro52 and Ro60 allowing autoimmunization, presumably as a result of normal cell turnover or specific injury in vivo.

The immune response to 52-kDa Ro and 60-kDa Ro is linked in experimental autoimmunity

Clustering of autoantibody specificities is a consistent finding in patients with systemic autoimmune diseases. Patients with Sjögren's syndrome frequently have autoantibodies to La, 60-kDa Ro(SS-A) protein (Ro60), and 52-kDa Ro(SS-A) protein (Ro52). In the case of anti-Ro60 and anti-La, there is evidence that these specificities occur together because of the physical association of the Ro60 and La proteins that form a ribonucleoprotein particle (RNP). Thus, the autoantibody response may spread from a single epitope to involve new epitopes located within other components of the RNP. The physical association of Ro52 with the Ro/La RNP has remained controversial, implying that Abs to Ro52 are not a consequence of intermolecular spreading and may be triggered independently of the anti-Ro60 response. To examine this relationship of the immune response to Ro52 and Ro60, mice were immunized with recombinant Ro52, Ro60, or La, and examined for autoantibody production. Immunization with Ro52 resulted in rapid, high titer Ab production to Ro52, followed 7 to 14 days later by lower titer autoantibody production to Ro60. Immunization with Ro60 led to anti-Ro60, which was also followed 7 to 14 days later by a lower titer anti-Ro52 response. Cross-reactivity of affinity-purified Abs from immune mouse sera was not observed. These observations suggest that the autoimmune responses to Ro60 and Ro52 are linked intrinsically, despite previous evidence suggesting they are not associated in vivo. The mechanism of linkage remains unclear, but the data are most consistent with some physical association of Ro52 and Ro60 allowing autoimmunization, presumably as a result of normal cell turnover or specific injury in vivo.

Nonprecipitating anti-La(SS-B) autoantibodies in primary Sjögren's syndrome

Anti-La(SS-B) precipitin-negative sera show a restricted epitope recognition and can be easily overlooked in routine laboratory testing. We have therefore determined the prevalence of nonprecipitating anti-La(SS-B) antibodies in patients with primary Sjögren's syndrome and studied their clinical and immunological associations. Clinical details were obtained from 68 patients with primary Sjögren's syndrome, and serum samples were examined by enzyme-linked immunosorbent assay using purified recombinant La, 60-kDa Ro, and 52-kDa Ro proteins and by counterimmunoelectrophoresis. Thirteen patients (19%) were identified with anti-La antibodies which were nonprecipitating. These patients had similar clinical findings to other groups of patients with Sjogren's syndrome, but had significantly lower rheumatoid factor and serum IgG levels than patients with anti-La precipitins. None of the patients with nonprecipitating anti-La antibodies had previously contained anti-La precipitins in their sera. Furthermore, they tended to have lower levels of antibodies directed against denatured 60-kDa Ro (but not 52-kDa Ro) compared with anti-La precipitin-positive patients. Patients with Sjögren's syndrome associated with nonprecipitating anti-La antibodies represent a stable serological and clinical subset in which there appears to be limited diversification of the autoimmune response to the Ro60 and La proteins of the Ro/La ribonucleoprotein.

Structural differences between the human and mouse 52-kD Ro autoantigens associated with poorly conserved autoantibody activity across species

Anti-nuclear autoantibodies found in human autoimmune diseases frequently cross-react with homologous autoantigens in distant species, supporting the notion that autoantibodies target conserved functional domains. However, the 52-kD Ro(SS-A) protein is an exception, in that human autoantibodies are not known to recognize any equivalent antigen in the cells of rodents and other non-primate species. To understand this lack of cross-reactivity we have isolated cDNAs encoding the mouse 52-kD Ro molecule. The cDNA encoding mouse 52-kD Ro revealed an open reading frame of 470 amino acids, with 70% sequence identity to the human 52-kD Ro antigen. The putative leucine-zipper and zinc-finger motifs present in human Ro52 were conserved in the mouse protein. Recombinant mouse 52-kD Ro protein reacted with human autoantibodies by ELISA and immunoblot, but with approximately 10-fold lower reactivity than recombinant human 52-kD Ro protein under the same conditions. Detection of both human and mouse 52-kD Ro by immunoblot was dependent on antigen concentration which was limiting in the cell equivalents generally used in immunoblot assays. Differential chaotropic disruption of antibody binding suggested a lower avidity of human autoantibody binding to the mouse 52-kD Ro protein compared with the human antigen. Thus the poor reactivity of native mouse 52-kD Ro with human autoantibodies is associated with species divergence diffusely distributed throughout the primary structure of the 52-kD Ro molecule.

Effect of companions in modulating stress associated with new group formation in juvenile rhesus macaques

To determine if the presence of one or more familiar peers buffers the physiological effect of a stressor, 10 juvenile rhesus monkeys were removed from their natal group and placed together to form a new peer group. Six of the 10 juveniles were from the natal group of one or more others (companion subjects) whereas four juveniles came from entirely separate natal groups (alone subjects). Moreover, six matched juveniles remained in their natal group serving as controls. Two baseline blood samples were collected from all subjects, and then at 24 h, 1 week, and 4 weeks following the peer group formation. There was a significant interaction among the three study groups and sample times for absolute numbers of helper/inducer T lymphocytes, suppressor/cytotoxic T lymphocytes, and B lymphocytes, but not cortisol concentrations. Planned post hoc comparisons found that subjects introduced to the peer group, both those alone and those with companion(s), showed a significantly greater decline from baseline in lymphocyte subsets 24 h later compared to control subjects. It is of note that the alone subjects showed a significantly greater percent decline from baseline in helper/inducer T lymphocytes than companion subjects at 24 h, but not in suppressor/cytotoxic T lymphocytes or B lymphocytes, Planned post hoc comparisons for cortisol found that alone subjects showed significantly higher cortisol concentrations than those subjects with a companion only at the 1-week sample point. Proximity accounted for a significant portion of the variation (R = 0.66) in percent change in helper/inducer T lymphocytes at 24 h and this was a result of the companion subjects staying together. Results of this study confirm the stressful effect of removal from the natal group to a new social situation in juvenile rhesus monkeys and also adds to the growing body of human and nonhuman primate literature that the presence of companions can modulate the physiological effects of a stressor.